Piston rings are well known. They are usually received within an annular groove disposed about an outer periphery of a piston. In turn, the piston is reciprocable within a cylinder. The piston compresses fluids such as gases within a combustion chamber of the cylinder. In the case of an internal combustion engine, these fluids are ignited and expand, forcing the piston away from the point of ignition. The primary function of the piston ring is to provide an effective seal of the combustion gases, called "blow-by control". A secondary function of the piston ring is to prevent excess lubricating oil from entering the combustion chamber. To accomplish these sealing functions, the piston ring must constantly and fully contact the cylinder. Expanding gases tend to force the piston ring radially outwardly against the cylinder which aids in sealing. However, the design of the piston ring also plays an important role in sealing.
It is known to design a piston ring having a cross section in the shape of a keystone, i.e. a trapezoid. The keystone shape allows the expanding gases to more easily force the piston ring radially outwardly.
It is also known to taper an entire outer peripheral surface of a piston ring. The taper is provided for initial break-in only and is designed to have point contact between the piston ring and cylinder. After wearing in of the piston ring, the entire outer peripheral face fully contacts the cylinder.
In another known piston ring there is a projection at the uppermost portion of the outer peripheral face which is designed to wear away during initial break-in. After break-in, the entire outer peripheral surface acts as the sealing surface.
None of the prior art piston rings have a hardened sealing land that projects from the outer peripheral surface designed to seal against the cylinder during the entire service life of the piston ring. Moreover, none of the prior art designs taper only a portion of the outer peripheral surface in combination with a sealing land. Finally, prior art piston rings do not have an orientation feature that ensures proper orientation during installation.